1. Field of the Invention
Sulfur is found admixed with a wide variety of fossil fuels and metal ores. When oxidizing the naturally occurring minerals and fuels through heating or burning, the sulfur oxidation product is sulfur dioxide. Sulfur dioxide is a serious pollutant, since in itself it forms sulfurous acid, which in itself and also upon oxidation to sulfuric acid causes serious contamination and injurious effects to the environment.
One of the ways to prevent sulfur dioxide in waste gases from being vented to the atmosphere is to treat sulfur dioxide containing gaseous effluents with base, either in the liquid or vapor phase. Various bases have been used, such as soda ash, lime and the like.
There are a number of considerations in the choice and manner in which the base is employed. The first consideration is economics. There are a number of factors involved with the economics. One factor is the cost of the alkaline or basic material. A second factor is the efficiency of the alkaline material. The less efficient the material, the more costly the removal of sulfur dioxide will be, in requiring greater amounts than stoichiometric to provide for the desired reduction in sulfur dioxide in the effluent and in requiring larger plant, particularly storage, metering and recovery equipment. A third consideration is the degree to which the sulfur dioxide may be removed with a given amount of the base.
Besides the base which is employed, another consideration is the equipment required for processing and the effect of the materials employed on the equipment. There is also the nature of the sludge or residue and the manner in which the residue may be disposed of, as well as the condition e.g., temperature, of the effluent gas.
In developing a process for removing sulfur dioxide from effluent gases, normally flue gases, all of the above considerations are involved for an effective process. In view of the very large volumes of gas which exit from power plants, processing plants, and other installations burning or oxidizing sulfur containing materials, small improvements in efficiency can result in dramatic savings. It is therefore desirable to provide for simple and efficient processes utilizing comparatively inexpensive materials, which can rapidly reduce sulfur dioxide content in waste gases and the like to acceptable levels while producing residues which are readily disposable.
2. Description of the Prior Art
Type S hydrated dolomitic lime, which is prepared from calcined dolomite, is available as a structural material from Flintkote Lime Products. Description of the preparation of Type S hydrated lime may be found in Boynton, Chemistry and Technology of Lime and Limestone, Interscience Publishers, New York, 1965, pages 167, 288-9, 302-307, 317-318, and 333-338. U.S. Pat. No. 4,046,856 describes a sulfur dioxide removal process employing magnesium with recycling of the magnesium as magnesium hydroxide. Other patents of interest describing processing of flue gas with basic materials include U.S. Pat. Nos. 2,068,882, 3,883,639, 3,941,378, 3,919,393, 3,991,172, 4,011,299, and 4,018,868. See also, C.A. 81, 6803u, 82, 63922r, 82 174821b, 84, 155093r, 84, 155095t and Ger. Offen. 2,412,372.